Enlarge iframes so that their height is 80% of the card's height and the aspect ratio remains the same
This is important for video presentations with the beamer, because Youtube videos cannot be shown in full view since the presentation mode already uses full view.
If the width of the displayed card is not sufficient to display the video in full view (without scrolling), the height of the iframe should be reduced while maintaining the aspect ratio until the video is fully visible.
See also my comment elsewhere: 16e6554c (comment 71362)